1. Field of the Invention
The present invention relates to a photoprinter printing a color image on roll paper having thermal color-developing layers for yellow, magenta and cyan formed on the roll paper.
2. Description of the Background Art
Japanese Patent Laying-Open Nos. 9-99572 and 2000-94725 disclose techniques regarding photoprinters printing a color image on roll paper having thermal color-developing layers for yellow, magenta and cyan formed on the roll paper. Conventional general photoprinters each have a thermal head, a fixing lamp for magenta images (hereinafter magenta image fixing lamp) and a fixing lamp for yellow images (hereinafter yellow image fixing lamp) that are arranged along a path along which the roll paper is fed. A color image is printed on the roll paper by the steps of:    (1) drawing out the roll paper toward a paper exit to the position where image formation is started (image formation start position);    (2) drawing back the roll paper toward a paper feed source while setting the temperature of the thermal head to a first temperature (at which respective thermal color-developing layers of magenta and cyan do not develop respective colors) to form a yellow image on the thermal color-developing layer for yellow;    (3) drawing out the roll paper toward the paper exit to the position where fixing of the yellow image is started (yellow image fixing start position);    (4) drawing back the roll paper toward the paper feed source while exposing the yellow image formed in step (2) with the yellow image fixing lamp and then fixing the yellow image;    (5) drawing out the roll paper toward the paper exit to the image formation start position;    (6) drawing back the roll paper toward the paper feed source while setting the temperature of the thermal head to a second temperature (at which the thermal color-developing layer for cyan does not develop the color) higher than the first temperature to form a magenta image on the thermal color-developing layer for magenta;    (7) drawing out the roll paper toward the paper exit to the position where fixing of the magenta image is completed (magenta image fixing complete position) while exposing the magenta image formed in step (6) with the magenta image fixing lamp and then fixing the magenta image;    (8) drawing back the roll paper toward the paper feed source while setting the temperature of the thermal head to a third temperature higher than the second temperature to form a cyan image on the thermal color-developing layer for cyan;    (9) drawing out the roll paper toward the paper exit, separating the image-formed part of the paper from the roll paper and discharging the separated paper; and    (10) drawing back the roll paper toward the paper feed source.
In the photoprinter, the above-described image formation start position is defined so that the rear end of a region of the roll paper on which the color image is to be printed (print region of the roll paper) is closer to the paper exit relative to the thermal head, the yellow image fixing start position is defined so that the rear end of the print region of the roll paper is closer to the paper exit relative to an exposure area of the yellow image fixing lamp, and the magenta image fixing complete position is defined so that the rear end of the print region of the roll paper is positioned at an exposure area of the magenta image fixing lamp.
The above-described conventional photoprinters transport the roll paper back and forth five times for printing the single color image. A resultant problem is a considerably long time required for successively printing a plurality of color images, for example, a plurality of photo images taken by a digital camera.